Welding Processes
The Welding Processes domain tests whether you can match process, transfer mode, gas, and consumable to a joint, and predict what a robot will and will not do with each. Expect items that give a joint, position, and thickness, then ask which mode or consumable applies.
GMAW transfer modes
- Short circuiting: low voltage and current, small wire, CO2-rich gas. Suits thin sheet and out-of-position work, but the low heat input makes cold lap and root lack of fusion the classic defects.
- Globular: the transition regime between short circuit and spray. Large irregular droplets, unstable arc, spatter. Robotic procedures generally avoid it.
- Spray: above a transition current in argon-rich mixtures, roughly 80 percent argon or more. Axial transfer, deep penetration, high deposition, but confined to flat and horizontal positions.
- Pulsed spray: current alternates between a peak that detaches one droplet and a background that sustains the arc. Average current and heat input are lower, so it suits out-of-position work, thin-to-thick joints, and paths where travel speed varies.
Consumables and shielding gas
- ER70S-6 to AWS A5.18 is the standard solid wire for carbon steel. The S means solid; the 6 designates higher manganese and silicon, which tolerates mill scale better than ER70S-3.
- Flux-cored wires follow AWS A5.20. E71T-1C is qualified with CO2, E71T-1M with mixed gas; the suffix is not interchangeable. Slag must be removed between passes, so the cell needs a cleaning step or an operator gate.
- 90Ar/10CO2 suits pulsed spray on steel; 75Ar/25CO2 is common for short circuiting; stainless usually runs a tri-mix or 98Ar/2O2 with matching 308L or 316L wire.
Worked example
A 1/8 in carbon steel lap joint in the horizontal position. Short circuiting with 0.035 in wire and 75/25 gas would run, but fast robotic travel and a cold, fast-freezing puddle invite lack of fusion at the lap. Pulsed spray with 0.035 in ER70S-6 and 90/10 keeps average current low enough to control the puddle while delivering a directed, penetrating arc. The decision rests on heat input per unit length, not on raw amperage.
Traps
Assuming any GMAW setup can spray; forgetting that CO2-rich gas will not spray at all; confusing the C and M suffixes on flux-cored wire; ignoring slag removal when cycle time is calculated.